Software defined radio

Software defined radio (SDR) is one of the things I am most curious about. There is just so much data being exchanged via radio these days. It’s strange to think about the constant complex pattern of broadcasting happening all around us.

This video gives a bit of a taste of what is happening in one part of the world and across a fairly narrow range of frequencies:

It’s pretty cool that he is able to identify and analyze Chinese over-the-horizon RADAR. It shows some of the possibilities SDR opens up for hobbyists.

You could do some very cool stuff with this: set up your own infrastructure independent computer networks, explore what sort of communication is happening around you, conduct intrusion detection (looking for interception devices broadcasting), and experiment with the security of your hardware, such as the Bluetooth chips in your phone and laptop.

A software-defined radio system, or SDR, is a radio communication system where components that have been typically implemented in hardware (e.g. mixers, filters, amplifiers, modulators/demodulators, detectors, etc.) are instead implemented by means of software on a personal computer or embedded computing devices. While the concept of SDR is not new, the rapidly evolving capabilities of digital electronics render practical many processes which used to be only theoretically possible.

A basic SDR system may consist of a personal computer equipped with a sound card, or other analog-to-digital converter, preceded by some form of RF front end. Significant amounts of signal processing are handed over to the general-purpose processor, rather than being done in special-purpose hardware. Such a design produces a radio which can receive and transmit widely different radio protocols (sometimes referred to as waveforms) based solely on the software used.

Software radios have significant utility for the military and cell phone services, both of which must serve a wide variety of changing radio protocols in real time.

In the long term, software-defined radios are expected by proponents like the SDRForum (now The Wireless Innovation Forum) to become the dominant technology in radio communications. SDRs, along with software defined antennas are the enablers of the cognitive radio.

In 1976, two shaggy-haired college dropouts founded a company called Apple to manufacture personal computers. The company’s prospects looked so poor that the third co-founder relinquished his 10 percent stake in the company for $800 that same year. It simply wasn’t clear why anyone would want the firm’s Apple I computer. It was so under-powered that it couldn’t perform many of the functions of mainframes and minicomputers that were already on the market. And most consumers had no interest in having a computer in their homes.

Today, of course, Apple is the world’s largest company by market capitalization. What was important about the Apple I wasn’t the meager capabilities of the original version, but the promise it held for rapid innovation in the coming decades.

Now, a company called Per Vices hopes to do for wireless communication what Apple did for computing. It is selling software-defined radio gear called the Phi that, like the Apple I, is likely to be of little interest to the average consumer (it was even briefly priced at the same point as the Apple I, $666.66, but has since been placed at $750). But the device, and others like it, has the potential to transform the wireless industry. This time, the revolution will depend on hackers enabled to manipulate radio signals in software.

A working USRP system comes in three parts: the main USRP box, an RF daughterboard, and a computer. The daughterboard handles the actual reception of radio signals, and passes the analog signal to the main USRP unit. Ettus explained to us what happens from there.

“First it converts the analog signal to digital. Then the digital signal is sent to a field-programmable gate array. The FPGA does the high-speed processing and the user can modify it and put all sorts of interesting things in there. In the most basic configuration, the FPGA reduces the sample rate, does some frequency translation, and then sends that out over the interface” to the CPU.

The interface that connects the USRP to the computer is the main thing that distinguishes the various USRP models from each other. The cheapest model (costing $650) delivers the data to the user’s computer over a relatively slow USB link. The priciest model (costing $1700) has a gigabit Ethernet interface. In between, the company offers an “embedded” model that includes a built-in CPU capable of running a full Linux distribution, which allows it to function as a stand-alone device.

Each RF daughterboard is designed to receive a different range of frequencies. “We used to need a lot of different daughterboards to cover an interesting frequency range,” he told us. “When we first started, you could only get a couple hundred MHz with decent performance. But as technology advanced, we’ve gotten newer and newer daughterboards with wider range.”

“Online hacktivist collective Anonymous has announced that it is working on a new tool called Airchat which could allow people to communicate without the need for a phone or an internet connection — using radio waves instead. Anonymous, the amorphous group best known for attacking high profile targets like Sony and the CIA in recent years, said on the project’s Github page: ‘Airchat is a free communication tool [that] doesn’t need internet infrastructure [or] a cell phone network. Instead it relies on any available radio link or device capable of transmitting audio.’ Despite the Airchat system being highly involved and too complex for most people in its current form, Anonymous says it has so far used it to play interactive chess games with people at 180 miles away; share pictures and even established encrypted low bandwidth digital voice chats. In order to get Airchat to work, you will need to have a handheld radio transceiver, a laptop running either Windows, Mac OS X or Linux, and be able to install and run several pieces of complex software.”

One reflector, which the NSA called Ragemaster, can be fixed to a computer’s monitor cable to pick up on-screen images. Another, Surlyspawn, sits on the keyboard cable and harvests keystrokes. After a lot of trial and error, Ossmann found these bugs can be remarkably simple devices – little more than a tiny transistor and a 2-centimetre-long wire acting as an antenna.